<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="generator" content="rustdoc">
    <meta name="description" content="Source to the Rust file `/home/fmp/.cargo/registry/src/github.com-1ecc6299db9ec823/regex-0.1.80/src/utf8.rs`.">
    <meta name="keywords" content="rust, rustlang, rust-lang">

    <title>utf8.rs.html -- source</title>

    <link rel="stylesheet" type="text/css" href="../../normalize.css">
    <link rel="stylesheet" type="text/css" href="../../rustdoc.css">
    <link rel="stylesheet" type="text/css" href="../../main.css">
    

    <link rel="shortcut icon" href="https://www.rust-lang.org/favicon.ico">
    
</head>
<body class="rustdoc source">
    <!--[if lte IE 8]>
    <div class="warning">
        This old browser is unsupported and will most likely display funky
        things.
    </div>
    <![endif]-->

    

    <nav class="sidebar">
        <a href='../../regex/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a>
        
    </nav>

    <nav class="sub">
        <form class="search-form js-only">
            <div class="search-container">
                <input class="search-input" name="search"
                       autocomplete="off"
                       placeholder="Click or press ‘S’ to search, ‘?’ for more options…"
                       type="search">
            </div>
        </form>
    </nav>

    <section id='main' class="content"><pre class="line-numbers"><span id="1">  1</span>
<span id="2">  2</span>
<span id="3">  3</span>
<span id="4">  4</span>
<span id="5">  5</span>
<span id="6">  6</span>
<span id="7">  7</span>
<span id="8">  8</span>
<span id="9">  9</span>
<span id="10"> 10</span>
<span id="11"> 11</span>
<span id="12"> 12</span>
<span id="13"> 13</span>
<span id="14"> 14</span>
<span id="15"> 15</span>
<span id="16"> 16</span>
<span id="17"> 17</span>
<span id="18"> 18</span>
<span id="19"> 19</span>
<span id="20"> 20</span>
<span id="21"> 21</span>
<span id="22"> 22</span>
<span id="23"> 23</span>
<span id="24"> 24</span>
<span id="25"> 25</span>
<span id="26"> 26</span>
<span id="27"> 27</span>
<span id="28"> 28</span>
<span id="29"> 29</span>
<span id="30"> 30</span>
<span id="31"> 31</span>
<span id="32"> 32</span>
<span id="33"> 33</span>
<span id="34"> 34</span>
<span id="35"> 35</span>
<span id="36"> 36</span>
<span id="37"> 37</span>
<span id="38"> 38</span>
<span id="39"> 39</span>
<span id="40"> 40</span>
<span id="41"> 41</span>
<span id="42"> 42</span>
<span id="43"> 43</span>
<span id="44"> 44</span>
<span id="45"> 45</span>
<span id="46"> 46</span>
<span id="47"> 47</span>
<span id="48"> 48</span>
<span id="49"> 49</span>
<span id="50"> 50</span>
<span id="51"> 51</span>
<span id="52"> 52</span>
<span id="53"> 53</span>
<span id="54"> 54</span>
<span id="55"> 55</span>
<span id="56"> 56</span>
<span id="57"> 57</span>
<span id="58"> 58</span>
<span id="59"> 59</span>
<span id="60"> 60</span>
<span id="61"> 61</span>
<span id="62"> 62</span>
<span id="63"> 63</span>
<span id="64"> 64</span>
<span id="65"> 65</span>
<span id="66"> 66</span>
<span id="67"> 67</span>
<span id="68"> 68</span>
<span id="69"> 69</span>
<span id="70"> 70</span>
<span id="71"> 71</span>
<span id="72"> 72</span>
<span id="73"> 73</span>
<span id="74"> 74</span>
<span id="75"> 75</span>
<span id="76"> 76</span>
<span id="77"> 77</span>
<span id="78"> 78</span>
<span id="79"> 79</span>
<span id="80"> 80</span>
<span id="81"> 81</span>
<span id="82"> 82</span>
<span id="83"> 83</span>
<span id="84"> 84</span>
<span id="85"> 85</span>
<span id="86"> 86</span>
<span id="87"> 87</span>
<span id="88"> 88</span>
<span id="89"> 89</span>
<span id="90"> 90</span>
<span id="91"> 91</span>
<span id="92"> 92</span>
<span id="93"> 93</span>
<span id="94"> 94</span>
<span id="95"> 95</span>
<span id="96"> 96</span>
<span id="97"> 97</span>
<span id="98"> 98</span>
<span id="99"> 99</span>
<span id="100">100</span>
<span id="101">101</span>
<span id="102">102</span>
<span id="103">103</span>
<span id="104">104</span>
<span id="105">105</span>
<span id="106">106</span>
<span id="107">107</span>
<span id="108">108</span>
<span id="109">109</span>
<span id="110">110</span>
<span id="111">111</span>
<span id="112">112</span>
<span id="113">113</span>
<span id="114">114</span>
<span id="115">115</span>
<span id="116">116</span>
<span id="117">117</span>
<span id="118">118</span>
<span id="119">119</span>
<span id="120">120</span>
<span id="121">121</span>
<span id="122">122</span>
<span id="123">123</span>
<span id="124">124</span>
<span id="125">125</span>
<span id="126">126</span>
<span id="127">127</span>
<span id="128">128</span>
<span id="129">129</span>
<span id="130">130</span>
<span id="131">131</span>
<span id="132">132</span>
<span id="133">133</span>
<span id="134">134</span>
<span id="135">135</span>
<span id="136">136</span>
<span id="137">137</span>
<span id="138">138</span>
<span id="139">139</span>
<span id="140">140</span>
<span id="141">141</span>
<span id="142">142</span>
<span id="143">143</span>
<span id="144">144</span>
<span id="145">145</span>
<span id="146">146</span>
<span id="147">147</span>
<span id="148">148</span>
<span id="149">149</span>
<span id="150">150</span>
<span id="151">151</span>
<span id="152">152</span>
<span id="153">153</span>
<span id="154">154</span>
<span id="155">155</span>
<span id="156">156</span>
<span id="157">157</span>
<span id="158">158</span>
<span id="159">159</span>
<span id="160">160</span>
<span id="161">161</span>
<span id="162">162</span>
<span id="163">163</span>
<span id="164">164</span>
<span id="165">165</span>
<span id="166">166</span>
<span id="167">167</span>
<span id="168">168</span>
<span id="169">169</span>
<span id="170">170</span>
<span id="171">171</span>
<span id="172">172</span>
<span id="173">173</span>
<span id="174">174</span>
<span id="175">175</span>
<span id="176">176</span>
<span id="177">177</span>
<span id="178">178</span>
<span id="179">179</span>
<span id="180">180</span>
<span id="181">181</span>
<span id="182">182</span>
<span id="183">183</span>
<span id="184">184</span>
<span id="185">185</span>
<span id="186">186</span>
<span id="187">187</span>
<span id="188">188</span>
<span id="189">189</span>
<span id="190">190</span>
<span id="191">191</span>
<span id="192">192</span>
<span id="193">193</span>
<span id="194">194</span>
<span id="195">195</span>
<span id="196">196</span>
<span id="197">197</span>
<span id="198">198</span>
<span id="199">199</span>
<span id="200">200</span>
<span id="201">201</span>
<span id="202">202</span>
<span id="203">203</span>
<span id="204">204</span>
<span id="205">205</span>
<span id="206">206</span>
<span id="207">207</span>
<span id="208">208</span>
<span id="209">209</span>
<span id="210">210</span>
<span id="211">211</span>
<span id="212">212</span>
<span id="213">213</span>
<span id="214">214</span>
<span id="215">215</span>
<span id="216">216</span>
<span id="217">217</span>
<span id="218">218</span>
<span id="219">219</span>
<span id="220">220</span>
<span id="221">221</span>
<span id="222">222</span>
<span id="223">223</span>
<span id="224">224</span>
<span id="225">225</span>
<span id="226">226</span>
<span id="227">227</span>
<span id="228">228</span>
<span id="229">229</span>
<span id="230">230</span>
<span id="231">231</span>
<span id="232">232</span>
<span id="233">233</span>
<span id="234">234</span>
<span id="235">235</span>
<span id="236">236</span>
<span id="237">237</span>
<span id="238">238</span>
<span id="239">239</span>
<span id="240">240</span>
<span id="241">241</span>
<span id="242">242</span>
<span id="243">243</span>
<span id="244">244</span>
<span id="245">245</span>
<span id="246">246</span>
<span id="247">247</span>
<span id="248">248</span>
<span id="249">249</span>
<span id="250">250</span>
<span id="251">251</span>
<span id="252">252</span>
<span id="253">253</span>
<span id="254">254</span>
<span id="255">255</span>
<span id="256">256</span>
<span id="257">257</span>
<span id="258">258</span>
<span id="259">259</span>
<span id="260">260</span>
<span id="261">261</span>
<span id="262">262</span>
<span id="263">263</span>
<span id="264">264</span>
<span id="265">265</span>
<span id="266">266</span>
<span id="267">267</span>
<span id="268">268</span>
<span id="269">269</span>
<span id="270">270</span>
</pre><pre class="rust ">
<span class="doccomment">/// A few elementary UTF-8 encoding and decoding functions used by the matching</span>
<span class="doccomment">/// engines.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// In an ideal world, the matching engines operate on `&amp;str` and we can just</span>
<span class="doccomment">/// lean on the standard library for all our UTF-8 needs. However, to support</span>
<span class="doccomment">/// byte based regexes (that can match on arbitrary bytes which may contain</span>
<span class="doccomment">/// UTF-8), we need to be capable of searching and decoding UTF-8 on a `&amp;[u8]`.</span>
<span class="doccomment">/// The standard library doesn&#39;t really recognize this use case, so we have</span>
<span class="doccomment">/// to build it out ourselves.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Should this be factored out into a separate crate? It seems independently</span>
<span class="doccomment">/// useful. There are other crates that already exist (e.g., `utf-8`) that have</span>
<span class="doccomment">/// overlapping use cases. Not sure what to do.</span>

<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">char</span>;

<span class="kw">const</span> <span class="ident">TAG_CONT</span>: <span class="ident">u8</span> <span class="op">=</span> <span class="number">0b1000_0000</span>;
<span class="kw">const</span> <span class="ident">TAG_TWO</span>: <span class="ident">u8</span> <span class="op">=</span> <span class="number">0b1100_0000</span>;
<span class="kw">const</span> <span class="ident">TAG_THREE</span>: <span class="ident">u8</span> <span class="op">=</span> <span class="number">0b1110_0000</span>;
<span class="kw">const</span> <span class="ident">TAG_FOUR</span>: <span class="ident">u8</span> <span class="op">=</span> <span class="number">0b1111_0000</span>;

<span class="doccomment">/// Returns the smallest possible index of the next valid UTF-8 sequence</span>
<span class="doccomment">/// starting after `i`.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">next_utf8</span>(<span class="ident">text</span>: <span class="kw-2">&amp;</span>[<span class="ident">u8</span>], <span class="ident">i</span>: <span class="ident">usize</span>) <span class="op">-&gt;</span> <span class="ident">usize</span> {
    <span class="kw">let</span> <span class="ident">b</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">text</span>.<span class="ident">get</span>(<span class="ident">i</span>) {
        <span class="prelude-val">None</span> <span class="op">=&gt;</span> <span class="kw">return</span> <span class="ident">i</span> <span class="op">+</span> <span class="number">1</span>,
        <span class="prelude-val">Some</span>(<span class="kw-2">&amp;</span><span class="ident">b</span>) <span class="op">=&gt;</span> <span class="ident">b</span>,
    };
    <span class="kw">let</span> <span class="ident">inc</span> <span class="op">=</span> <span class="kw">if</span> <span class="ident">b</span> <span class="op">&lt;=</span> <span class="number">0x7F</span> {
        <span class="number">1</span>
    } <span class="kw">else</span> <span class="kw">if</span> <span class="ident">b</span> <span class="op">&lt;=</span> <span class="number">0b110_11111</span> {
        <span class="number">2</span>
    } <span class="kw">else</span> <span class="kw">if</span> <span class="ident">b</span> <span class="op">&lt;=</span> <span class="number">0b1110_1111</span> {
        <span class="number">3</span>
    } <span class="kw">else</span> {
        <span class="number">4</span>
    };
    <span class="ident">i</span> <span class="op">+</span> <span class="ident">inc</span>
}

<span class="doccomment">/// Encode the given Unicode character to `dst` as a single UTF-8 sequence.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If `dst` is not long enough, then `None` is returned. Otherwise, the number</span>
<span class="doccomment">/// of bytes written is returned.</span>
<span class="attribute">#[<span class="ident">allow</span>(<span class="ident">dead_code</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">encode_utf8</span>(<span class="ident">character</span>: <span class="ident">char</span>, <span class="ident">dst</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> [<span class="ident">u8</span>]) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">usize</span><span class="op">&gt;</span> {
    <span class="kw">let</span> <span class="ident">code</span> <span class="op">=</span> <span class="ident">character</span> <span class="kw">as</span> <span class="ident">u32</span>;
    <span class="kw">if</span> <span class="ident">code</span> <span class="op">&lt;=</span> <span class="number">0x7F</span> <span class="op">&amp;&amp;</span> <span class="op">!</span><span class="ident">dst</span>.<span class="ident">is_empty</span>() {
        <span class="ident">dst</span>[<span class="number">0</span>] <span class="op">=</span> <span class="ident">code</span> <span class="kw">as</span> <span class="ident">u8</span>;
        <span class="prelude-val">Some</span>(<span class="number">1</span>)
    } <span class="kw">else</span> <span class="kw">if</span> <span class="ident">code</span> <span class="op">&lt;=</span> <span class="number">0x7FF</span> <span class="op">&amp;&amp;</span> <span class="ident">dst</span>.<span class="ident">len</span>() <span class="op">&gt;=</span> <span class="number">2</span> {
        <span class="ident">dst</span>[<span class="number">0</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&gt;&gt;</span> <span class="number">6</span> <span class="op">&amp;</span> <span class="number">0x1F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_TWO</span>;
        <span class="ident">dst</span>[<span class="number">1</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&amp;</span> <span class="number">0x3F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_CONT</span>;
        <span class="prelude-val">Some</span>(<span class="number">2</span>)
    } <span class="kw">else</span> <span class="kw">if</span> <span class="ident">code</span> <span class="op">&lt;=</span> <span class="number">0xFFFF</span> <span class="op">&amp;&amp;</span> <span class="ident">dst</span>.<span class="ident">len</span>() <span class="op">&gt;=</span> <span class="number">3</span>  {
        <span class="ident">dst</span>[<span class="number">0</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&gt;&gt;</span> <span class="number">12</span> <span class="op">&amp;</span> <span class="number">0x0F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_THREE</span>;
        <span class="ident">dst</span>[<span class="number">1</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&gt;&gt;</span>  <span class="number">6</span> <span class="op">&amp;</span> <span class="number">0x3F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_CONT</span>;
        <span class="ident">dst</span>[<span class="number">2</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&amp;</span> <span class="number">0x3F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_CONT</span>;
        <span class="prelude-val">Some</span>(<span class="number">3</span>)
    } <span class="kw">else</span> <span class="kw">if</span> <span class="ident">dst</span>.<span class="ident">len</span>() <span class="op">&gt;=</span> <span class="number">4</span> {
        <span class="ident">dst</span>[<span class="number">0</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&gt;&gt;</span> <span class="number">18</span> <span class="op">&amp;</span> <span class="number">0x07</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_FOUR</span>;
        <span class="ident">dst</span>[<span class="number">1</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&gt;&gt;</span> <span class="number">12</span> <span class="op">&amp;</span> <span class="number">0x3F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_CONT</span>;
        <span class="ident">dst</span>[<span class="number">2</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&gt;&gt;</span>  <span class="number">6</span> <span class="op">&amp;</span> <span class="number">0x3F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_CONT</span>;
        <span class="ident">dst</span>[<span class="number">3</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&amp;</span> <span class="number">0x3F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_CONT</span>;
        <span class="prelude-val">Some</span>(<span class="number">4</span>)
    } <span class="kw">else</span> {
        <span class="prelude-val">None</span>
    }
}

<span class="doccomment">/// Decode a single UTF-8 sequence into a single Unicode codepoint from `src`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If no valid UTF-8 sequence could be found, then `None` is returned.</span>
<span class="doccomment">/// Otherwise, the decoded codepoint and the number of bytes read is returned.</span>
<span class="doccomment">/// The number of bytes read (for a valid UTF-8 sequence) is guaranteed to be</span>
<span class="doccomment">/// 1, 2, 3 or 4.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that a UTF-8 sequence is invalid if it is incorrect UTF-8, encodes a</span>
<span class="doccomment">/// codepoint that is out of range (surrogate codepoints are out of range) or</span>
<span class="doccomment">/// is not the shortest possible UTF-8 sequence for that codepoint.</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">decode_utf8</span>(<span class="ident">src</span>: <span class="kw-2">&amp;</span>[<span class="ident">u8</span>]) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span>(<span class="ident">char</span>, <span class="ident">usize</span>)<span class="op">&gt;</span> {
    <span class="kw">let</span> <span class="ident">b0</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">src</span>.<span class="ident">get</span>(<span class="number">0</span>) {
        <span class="prelude-val">None</span> <span class="op">=&gt;</span> <span class="kw">return</span> <span class="prelude-val">None</span>,
        <span class="prelude-val">Some</span>(<span class="kw-2">&amp;</span><span class="ident">b</span>) <span class="kw">if</span> <span class="ident">b</span> <span class="op">&lt;=</span> <span class="number">0x7F</span> <span class="op">=&gt;</span> <span class="kw">return</span> <span class="prelude-val">Some</span>((<span class="ident">b</span> <span class="kw">as</span> <span class="ident">char</span>, <span class="number">1</span>)),
        <span class="prelude-val">Some</span>(<span class="kw-2">&amp;</span><span class="ident">b</span>) <span class="op">=&gt;</span> <span class="ident">b</span>,
    };
    <span class="kw">match</span> <span class="ident">b0</span> {
        <span class="number">0b110_00000</span> ... <span class="number">0b110_11111</span> <span class="op">=&gt;</span> {
            <span class="kw">if</span> <span class="ident">src</span>.<span class="ident">len</span>() <span class="op">&lt;</span> <span class="number">2</span> {
                <span class="kw">return</span> <span class="prelude-val">None</span>;
            }
            <span class="kw">let</span> <span class="ident">b1</span> <span class="op">=</span> <span class="ident">src</span>[<span class="number">1</span>];
            <span class="kw">let</span> <span class="ident">cp</span> <span class="op">=</span> ((<span class="ident">b0</span> <span class="op">&amp;</span> <span class="op">!</span><span class="ident">TAG_TWO</span>) <span class="kw">as</span> <span class="ident">u32</span>) <span class="op">&lt;&lt;</span> <span class="number">6</span>
                     <span class="op">|</span> ((<span class="ident">b1</span> <span class="op">&amp;</span> <span class="op">!</span><span class="ident">TAG_CONT</span>) <span class="kw">as</span> <span class="ident">u32</span>);
            <span class="kw">match</span> <span class="ident">cp</span> {
                <span class="number">0x80</span> ... <span class="number">0x7FF</span> <span class="op">=&gt;</span> <span class="ident">char</span>::<span class="ident">from_u32</span>(<span class="ident">cp</span>).<span class="ident">map</span>(<span class="op">|</span><span class="ident">cp</span><span class="op">|</span> (<span class="ident">cp</span>, <span class="number">2</span>)),
                _ <span class="op">=&gt;</span> <span class="prelude-val">None</span>,
            }
        }
        <span class="number">0b1110_0000</span> ... <span class="number">0b1110_1111</span> <span class="op">=&gt;</span> {
            <span class="kw">if</span> <span class="ident">src</span>.<span class="ident">len</span>() <span class="op">&lt;</span> <span class="number">3</span> {
                <span class="kw">return</span> <span class="prelude-val">None</span>;
            }
            <span class="kw">let</span> (<span class="ident">b1</span>, <span class="ident">b2</span>) <span class="op">=</span> (<span class="ident">src</span>[<span class="number">1</span>], <span class="ident">src</span>[<span class="number">2</span>]);
            <span class="kw">let</span> <span class="ident">cp</span> <span class="op">=</span> ((<span class="ident">b0</span> <span class="op">&amp;</span> <span class="op">!</span><span class="ident">TAG_THREE</span>) <span class="kw">as</span> <span class="ident">u32</span>) <span class="op">&lt;&lt;</span> <span class="number">12</span>
                     <span class="op">|</span> ((<span class="ident">b1</span> <span class="op">&amp;</span> <span class="op">!</span><span class="ident">TAG_CONT</span>) <span class="kw">as</span> <span class="ident">u32</span>) <span class="op">&lt;&lt;</span> <span class="number">6</span>
                     <span class="op">|</span> ((<span class="ident">b2</span> <span class="op">&amp;</span> <span class="op">!</span><span class="ident">TAG_CONT</span>) <span class="kw">as</span> <span class="ident">u32</span>);
            <span class="kw">match</span> <span class="ident">cp</span> {
                <span class="comment">// char::from_u32 will disallow surrogate codepoints.</span>
                <span class="number">0x800</span> ... <span class="number">0xFFFF</span> <span class="op">=&gt;</span> <span class="ident">char</span>::<span class="ident">from_u32</span>(<span class="ident">cp</span>).<span class="ident">map</span>(<span class="op">|</span><span class="ident">cp</span><span class="op">|</span> (<span class="ident">cp</span>, <span class="number">3</span>)),
                _ <span class="op">=&gt;</span> <span class="prelude-val">None</span>,
            }
        }
        <span class="number">0b11110_000</span> ... <span class="number">0b11110_111</span> <span class="op">=&gt;</span> {
            <span class="kw">if</span> <span class="ident">src</span>.<span class="ident">len</span>() <span class="op">&lt;</span> <span class="number">4</span> {
                <span class="kw">return</span> <span class="prelude-val">None</span>;
            }
            <span class="kw">let</span> (<span class="ident">b1</span>, <span class="ident">b2</span>, <span class="ident">b3</span>) <span class="op">=</span> (<span class="ident">src</span>[<span class="number">1</span>], <span class="ident">src</span>[<span class="number">2</span>], <span class="ident">src</span>[<span class="number">3</span>]);
            <span class="kw">let</span> <span class="ident">cp</span> <span class="op">=</span> ((<span class="ident">b0</span> <span class="op">&amp;</span> <span class="op">!</span><span class="ident">TAG_FOUR</span>) <span class="kw">as</span> <span class="ident">u32</span>) <span class="op">&lt;&lt;</span> <span class="number">18</span>
                     <span class="op">|</span> ((<span class="ident">b1</span> <span class="op">&amp;</span> <span class="op">!</span><span class="ident">TAG_CONT</span>) <span class="kw">as</span> <span class="ident">u32</span>) <span class="op">&lt;&lt;</span> <span class="number">12</span>
                     <span class="op">|</span> ((<span class="ident">b2</span> <span class="op">&amp;</span> <span class="op">!</span><span class="ident">TAG_CONT</span>) <span class="kw">as</span> <span class="ident">u32</span>) <span class="op">&lt;&lt;</span> <span class="number">6</span>
                     <span class="op">|</span> ((<span class="ident">b3</span> <span class="op">&amp;</span> <span class="op">!</span><span class="ident">TAG_CONT</span>) <span class="kw">as</span> <span class="ident">u32</span>);
            <span class="kw">match</span> <span class="ident">cp</span> {
                <span class="number">0x10000</span> ... <span class="number">0x10FFFF</span> <span class="op">=&gt;</span> <span class="ident">char</span>::<span class="ident">from_u32</span>(<span class="ident">cp</span>).<span class="ident">map</span>(<span class="op">|</span><span class="ident">cp</span><span class="op">|</span> (<span class="ident">cp</span>, <span class="number">4</span>)),
                _ <span class="op">=&gt;</span> <span class="prelude-val">None</span>,
            }
        }
        _ <span class="op">=&gt;</span> <span class="prelude-val">None</span>,
    }
}

<span class="doccomment">/// Like decode_utf8, but decodes the last UTF-8 sequence in `src` instead of</span>
<span class="doccomment">/// the first.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">decode_last_utf8</span>(<span class="ident">src</span>: <span class="kw-2">&amp;</span>[<span class="ident">u8</span>]) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span>(<span class="ident">char</span>, <span class="ident">usize</span>)<span class="op">&gt;</span> {
    <span class="kw">if</span> <span class="ident">src</span>.<span class="ident">is_empty</span>() {
        <span class="kw">return</span> <span class="prelude-val">None</span>;
    }
    <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">start</span> <span class="op">=</span> <span class="ident">src</span>.<span class="ident">len</span>() <span class="op">-</span> <span class="number">1</span>;
    <span class="kw">if</span> <span class="ident">src</span>[<span class="ident">start</span>] <span class="op">&lt;=</span> <span class="number">0x7F</span> {
        <span class="kw">return</span> <span class="prelude-val">Some</span>((<span class="ident">src</span>[<span class="ident">start</span>] <span class="kw">as</span> <span class="ident">char</span>, <span class="number">1</span>));
    }
    <span class="kw">while</span> <span class="ident">start</span> <span class="op">&gt;</span> <span class="ident">src</span>.<span class="ident">len</span>().<span class="ident">saturating_sub</span>(<span class="number">4</span>) {
        <span class="ident">start</span> <span class="op">-=</span> <span class="number">1</span>;
        <span class="kw">if</span> <span class="ident">is_start_byte</span>(<span class="ident">src</span>[<span class="ident">start</span>]) {
            <span class="kw">break</span>;
        }
    }
    <span class="kw">match</span> <span class="ident">decode_utf8</span>(<span class="kw-2">&amp;</span><span class="ident">src</span>[<span class="ident">start</span>..]) {
        <span class="prelude-val">None</span> <span class="op">=&gt;</span> <span class="prelude-val">None</span>,
        <span class="prelude-val">Some</span>((_, <span class="ident">n</span>)) <span class="kw">if</span> <span class="ident">n</span> <span class="op">&lt;</span> <span class="ident">src</span>.<span class="ident">len</span>() <span class="op">-</span> <span class="ident">start</span> <span class="op">=&gt;</span> <span class="prelude-val">None</span>,
        <span class="prelude-val">Some</span>((<span class="ident">cp</span>, <span class="ident">n</span>)) <span class="op">=&gt;</span> <span class="prelude-val">Some</span>((<span class="ident">cp</span>, <span class="ident">n</span>)),
    }
}

<span class="kw">fn</span> <span class="ident">is_start_byte</span>(<span class="ident">b</span>: <span class="ident">u8</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
    <span class="ident">b</span> <span class="op">&amp;</span> <span class="number">0b11_000000</span> <span class="op">!=</span> <span class="number">0b1_0000000</span>
}

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span>
<span class="kw">mod</span> <span class="ident">tests</span> {
    <span class="kw">use</span> <span class="ident">std</span>::<span class="ident">str</span>;

    <span class="kw">use</span> <span class="ident">quickcheck</span>::<span class="ident">quickcheck</span>;

    <span class="kw">use</span> <span class="kw">super</span>::{
        <span class="ident">TAG_CONT</span>, <span class="ident">TAG_TWO</span>, <span class="ident">TAG_THREE</span>, <span class="ident">TAG_FOUR</span>,
        <span class="ident">decode_utf8</span>, <span class="ident">decode_last_utf8</span>, <span class="ident">encode_utf8</span>,
    };

    <span class="attribute">#[<span class="ident">test</span>]</span>
    <span class="kw">fn</span> <span class="ident">prop_roundtrip</span>() {
        <span class="kw">fn</span> <span class="ident">p</span>(<span class="ident">given_cp</span>: <span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
            <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">tmp</span> <span class="op">=</span> [<span class="number">0</span>; <span class="number">4</span>];
            <span class="kw">let</span> <span class="ident">encoded_len</span> <span class="op">=</span> <span class="ident">encode_utf8</span>(<span class="ident">given_cp</span>, <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">tmp</span>).<span class="ident">unwrap</span>();
            <span class="kw">let</span> (<span class="ident">got_cp</span>, <span class="ident">got_len</span>) <span class="op">=</span> <span class="ident">decode_utf8</span>(<span class="kw-2">&amp;</span><span class="ident">tmp</span>[..<span class="ident">encoded_len</span>]).<span class="ident">unwrap</span>();
            <span class="ident">encoded_len</span> <span class="op">==</span> <span class="ident">got_len</span> <span class="op">&amp;&amp;</span> <span class="ident">given_cp</span> <span class="op">==</span> <span class="ident">got_cp</span>
        }
        <span class="ident">quickcheck</span>(<span class="ident">p</span> <span class="kw">as</span> <span class="kw">fn</span>(<span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">bool</span>)
    }

    <span class="attribute">#[<span class="ident">test</span>]</span>
    <span class="kw">fn</span> <span class="ident">prop_roundtrip_last</span>() {
        <span class="kw">fn</span> <span class="ident">p</span>(<span class="ident">given_cp</span>: <span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
            <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">tmp</span> <span class="op">=</span> [<span class="number">0</span>; <span class="number">4</span>];
            <span class="kw">let</span> <span class="ident">encoded_len</span> <span class="op">=</span> <span class="ident">encode_utf8</span>(<span class="ident">given_cp</span>, <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">tmp</span>).<span class="ident">unwrap</span>();
            <span class="kw">let</span> (<span class="ident">got_cp</span>, <span class="ident">got_len</span>) <span class="op">=</span>
                <span class="ident">decode_last_utf8</span>(<span class="kw-2">&amp;</span><span class="ident">tmp</span>[..<span class="ident">encoded_len</span>]).<span class="ident">unwrap</span>();
            <span class="ident">encoded_len</span> <span class="op">==</span> <span class="ident">got_len</span> <span class="op">&amp;&amp;</span> <span class="ident">given_cp</span> <span class="op">==</span> <span class="ident">got_cp</span>
        }
        <span class="ident">quickcheck</span>(<span class="ident">p</span> <span class="kw">as</span> <span class="kw">fn</span>(<span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">bool</span>)
    }

    <span class="attribute">#[<span class="ident">test</span>]</span>
    <span class="kw">fn</span> <span class="ident">prop_encode_matches_std</span>() {
        <span class="kw">fn</span> <span class="ident">p</span>(<span class="ident">cp</span>: <span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
            <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">got</span> <span class="op">=</span> [<span class="number">0</span>; <span class="number">4</span>];
            <span class="kw">let</span> <span class="ident">n</span> <span class="op">=</span> <span class="ident">encode_utf8</span>(<span class="ident">cp</span>, <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">got</span>).<span class="ident">unwrap</span>();
            <span class="kw">let</span> <span class="ident">expected</span> <span class="op">=</span> <span class="ident">cp</span>.<span class="ident">to_string</span>();
            <span class="kw-2">&amp;</span><span class="ident">got</span>[..<span class="ident">n</span>] <span class="op">==</span> <span class="ident">expected</span>.<span class="ident">as_bytes</span>()
        }
        <span class="ident">quickcheck</span>(<span class="ident">p</span> <span class="kw">as</span> <span class="kw">fn</span>(<span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">bool</span>)
    }

    <span class="attribute">#[<span class="ident">test</span>]</span>
    <span class="kw">fn</span> <span class="ident">prop_decode_matches_std</span>() {
        <span class="kw">fn</span> <span class="ident">p</span>(<span class="ident">given_cp</span>: <span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
            <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">tmp</span> <span class="op">=</span> [<span class="number">0</span>; <span class="number">4</span>];
            <span class="kw">let</span> <span class="ident">n</span> <span class="op">=</span> <span class="ident">encode_utf8</span>(<span class="ident">given_cp</span>, <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">tmp</span>).<span class="ident">unwrap</span>();
            <span class="kw">let</span> (<span class="ident">got_cp</span>, _) <span class="op">=</span> <span class="ident">decode_utf8</span>(<span class="kw-2">&amp;</span><span class="ident">tmp</span>[..<span class="ident">n</span>]).<span class="ident">unwrap</span>();
            <span class="kw">let</span> <span class="ident">expected_cp</span> <span class="op">=</span>
                <span class="ident">str</span>::<span class="ident">from_utf8</span>(<span class="kw-2">&amp;</span><span class="ident">tmp</span>[..<span class="ident">n</span>]).<span class="ident">unwrap</span>().<span class="ident">chars</span>().<span class="ident">next</span>().<span class="ident">unwrap</span>();
            <span class="ident">got_cp</span> <span class="op">==</span> <span class="ident">expected_cp</span>
        }
        <span class="ident">quickcheck</span>(<span class="ident">p</span> <span class="kw">as</span> <span class="kw">fn</span>(<span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">bool</span>)
    }

    <span class="attribute">#[<span class="ident">test</span>]</span>
    <span class="kw">fn</span> <span class="ident">prop_decode_last_matches_std</span>() {
        <span class="kw">fn</span> <span class="ident">p</span>(<span class="ident">given_cp</span>: <span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
            <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">tmp</span> <span class="op">=</span> [<span class="number">0</span>; <span class="number">4</span>];
            <span class="kw">let</span> <span class="ident">n</span> <span class="op">=</span> <span class="ident">encode_utf8</span>(<span class="ident">given_cp</span>, <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">tmp</span>).<span class="ident">unwrap</span>();
            <span class="kw">let</span> (<span class="ident">got_cp</span>, _) <span class="op">=</span> <span class="ident">decode_last_utf8</span>(<span class="kw-2">&amp;</span><span class="ident">tmp</span>[..<span class="ident">n</span>]).<span class="ident">unwrap</span>();
            <span class="kw">let</span> <span class="ident">expected_cp</span> <span class="op">=</span>
                <span class="ident">str</span>::<span class="ident">from_utf8</span>(<span class="kw-2">&amp;</span><span class="ident">tmp</span>[..<span class="ident">n</span>]).<span class="ident">unwrap</span>()
                    .<span class="ident">chars</span>().<span class="ident">rev</span>().<span class="ident">next</span>().<span class="ident">unwrap</span>();
            <span class="ident">got_cp</span> <span class="op">==</span> <span class="ident">expected_cp</span>
        }
        <span class="ident">quickcheck</span>(<span class="ident">p</span> <span class="kw">as</span> <span class="kw">fn</span>(<span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">bool</span>)
    }

    <span class="attribute">#[<span class="ident">test</span>]</span>
    <span class="kw">fn</span> <span class="ident">reject_invalid</span>() {
        <span class="comment">// Invalid start byte</span>
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_utf8</span>(<span class="kw-2">&amp;</span>[<span class="number">0xFF</span>]), <span class="prelude-val">None</span>);
        <span class="comment">// Surrogate pair</span>
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_utf8</span>(<span class="kw-2">&amp;</span>[<span class="number">0xED</span>, <span class="number">0xA0</span>, <span class="number">0x81</span>]), <span class="prelude-val">None</span>);
        <span class="comment">// Bad lengths</span>
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_utf8</span>(<span class="kw-2">&amp;</span>[<span class="number">0xC3</span>]), <span class="prelude-val">None</span>); <span class="comment">// 2 bytes</span>
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_utf8</span>(<span class="kw-2">&amp;</span>[<span class="number">0xEF</span>, <span class="number">0xBF</span>]), <span class="prelude-val">None</span>); <span class="comment">// 3 bytes</span>
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_utf8</span>(<span class="kw-2">&amp;</span>[<span class="number">0xF4</span>, <span class="number">0x8F</span>, <span class="number">0xBF</span>]), <span class="prelude-val">None</span>); <span class="comment">// 4 bytes</span>
        <span class="comment">// Not a minimal UTF-8 sequence</span>
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_utf8</span>(<span class="kw-2">&amp;</span>[<span class="ident">TAG_TWO</span>, <span class="ident">TAG_CONT</span> <span class="op">|</span> <span class="string">b&#39;a&#39;</span>]), <span class="prelude-val">None</span>);
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_utf8</span>(<span class="kw-2">&amp;</span>[<span class="ident">TAG_THREE</span>, <span class="ident">TAG_CONT</span>, <span class="ident">TAG_CONT</span> <span class="op">|</span> <span class="string">b&#39;a&#39;</span>]), <span class="prelude-val">None</span>);
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_utf8</span>(<span class="kw-2">&amp;</span>[
            <span class="ident">TAG_FOUR</span>, <span class="ident">TAG_CONT</span>, <span class="ident">TAG_CONT</span>, <span class="ident">TAG_CONT</span> <span class="op">|</span> <span class="string">b&#39;a&#39;</span>,
        ]), <span class="prelude-val">None</span>);
    }

    <span class="attribute">#[<span class="ident">test</span>]</span>
    <span class="kw">fn</span> <span class="ident">reject_invalid_last</span>() {
        <span class="comment">// Invalid start byte</span>
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_last_utf8</span>(<span class="kw-2">&amp;</span>[<span class="number">0xFF</span>]), <span class="prelude-val">None</span>);
        <span class="comment">// Surrogate pair</span>
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_last_utf8</span>(<span class="kw-2">&amp;</span>[<span class="number">0xED</span>, <span class="number">0xA0</span>, <span class="number">0x81</span>]), <span class="prelude-val">None</span>);
        <span class="comment">// Bad lengths</span>
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_last_utf8</span>(<span class="kw-2">&amp;</span>[<span class="number">0xC3</span>]), <span class="prelude-val">None</span>); <span class="comment">// 2 bytes</span>
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_last_utf8</span>(<span class="kw-2">&amp;</span>[<span class="number">0xEF</span>, <span class="number">0xBF</span>]), <span class="prelude-val">None</span>); <span class="comment">// 3 bytes</span>
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_last_utf8</span>(<span class="kw-2">&amp;</span>[<span class="number">0xF4</span>, <span class="number">0x8F</span>, <span class="number">0xBF</span>]), <span class="prelude-val">None</span>); <span class="comment">// 4 bytes</span>
        <span class="comment">// Not a minimal UTF-8 sequence</span>
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_last_utf8</span>(<span class="kw-2">&amp;</span>[<span class="ident">TAG_TWO</span>, <span class="ident">TAG_CONT</span> <span class="op">|</span> <span class="string">b&#39;a&#39;</span>]), <span class="prelude-val">None</span>);
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_last_utf8</span>(<span class="kw-2">&amp;</span>[
            <span class="ident">TAG_THREE</span>, <span class="ident">TAG_CONT</span>, <span class="ident">TAG_CONT</span> <span class="op">|</span> <span class="string">b&#39;a&#39;</span>,
        ]), <span class="prelude-val">None</span>);
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decode_last_utf8</span>(<span class="kw-2">&amp;</span>[
            <span class="ident">TAG_FOUR</span>, <span class="ident">TAG_CONT</span>, <span class="ident">TAG_CONT</span>, <span class="ident">TAG_CONT</span> <span class="op">|</span> <span class="string">b&#39;a&#39;</span>,
        ]), <span class="prelude-val">None</span>);
    }
}
</pre>
</section>
    <section id='search' class="content hidden"></section>

    <section class="footer"></section>

    <aside id="help" class="hidden">
        <div>
            <h1 class="hidden">Help</h1>

            <div class="shortcuts">
                <h2>Keyboard Shortcuts</h2>

                <dl>
                    <dt>?</dt>
                    <dd>Show this help dialog</dd>
                    <dt>S</dt>
                    <dd>Focus the search field</dd>
                    <dt>&larrb;</dt>
                    <dd>Move up in search results</dd>
                    <dt>&rarrb;</dt>
                    <dd>Move down in search results</dd>
                    <dt>&#9166;</dt>
                    <dd>Go to active search result</dd>
                    <dt>+</dt>
                    <dd>Collapse/expand all sections</dd>
                </dl>
            </div>

            <div class="infos">
                <h2>Search Tricks</h2>

                <p>
                    Prefix searches with a type followed by a colon (e.g.
                    <code>fn:</code>) to restrict the search to a given type.
                </p>

                <p>
                    Accepted types are: <code>fn</code>, <code>mod</code>,
                    <code>struct</code>, <code>enum</code>,
                    <code>trait</code>, <code>type</code>, <code>macro</code>,
                    and <code>const</code>.
                </p>

                <p>
                    Search functions by type signature (e.g.
                    <code>vec -> usize</code> or <code>* -> vec</code>)
                </p>
            </div>
        </div>
    </aside>

    

    <script>
        window.rootPath = "../../";
        window.currentCrate = "regex";
    </script>
    <script src="../../main.js"></script>
    <script defer src="../../search-index.js"></script>
</body>
</html>